Refrigerated case with low frost operation

ABSTRACT

An open-front refrigerated case with reduced frost operation includes a housing having an open front and defining a product storage space therein. An air flow device is operatively coupled to an air flow path to direct a flow of air over a dehumidification coil for discharge as a dehumidified air curtain over the open front. The dehumidification coil operates substantially frost-free at a temperature of greater than 32° F. A contact cooling device and/or a gravity cooling device is disposed within the space and arranged to receive a coolant from a coolant system, where the dehumidified air curtain operates as a humidity tempering boundary to minimize the humidity within the storage space, so that the case operates in a substantially frost-free manner.

BACKGROUND

The present invention relates to an open-front refrigerated case. Thepresent invention more specifically relates to an open-frontrefrigerated display case having chilled shelves and/or a gravitycooling coil. The present invention more specifically relates to anopen-front refrigerated display case having chilled shelves and/or agravity cooling coil, and an air curtain dehumidified by a dehumidifyingcoil operating above 32° F. that prevents frost formation on thedehumidifying coil and provides a low humidity boundary to minimizefrost formation on the chilled shelves and/or gravity cooling coil.

It is known to provide for a refrigerated case for storage andpresentation of food products (such as perishable meat, dairy, seafood,produce, etc.). Such known refrigerated cases may include those of atype typically having an open front to permit consumers to reach in andselect products from shelves within the case (e.g. “self service” typecases, etc.). Open-front refrigerated cases often have a main coolingcoil operating at a temperature below 32° F. to chill air that isdistributed by a fan through ducts. The chilled air is blown into theproduct storage space of the case for cooling the products, anddownwardly from a discharge along a top front portion of the case toprovide an “air curtain” extending across the front of the case. The aircurtain is intended to form an “invisible thermal boundary” between thechilled product storage space within the case and the warmer ambient airsurrounding a front of the case. The invisible thermal boundary of theair curtain is intended to minimize “mixing” of surroundingambient-temperature air with the chilled air within the storage space ofthe case and behind the air-curtain. However, the operation of the maincooling coil at a temperature below 32° F. tends to result in frostbuildup on the cooling coil over time as moisture in the air condensesand freezes on the surfaces of the cooling coil, resulting in diminishedperformance of the coil and increased energy consumption.

It is also known to provide refrigerated cases with chilled shelves orpans to provide contact cooling for food products stored and displayedon the shelves. Such cases are typically service-type cases that arenormally “closed” and provide access through doors or the like tominimize the amount of moisture accumulation within the storage space.However, such chilled pans also tend to accumulate frost over time asmoisture in the air space within the case (and from the ambient air whendoors to the case are opened) and from the food products condenses andfreezes on the chilled shelves.

It is also known to provide refrigerated cases with gravity-type coolingcoils located in a top portion of the case. Such cases are alsotypically service-type cases that are normally “closed” and provideaccess through doors or the like to minimize the amount of moistureaccumulation within the storage space, and to permit a naturalcirculation of air within the space as cooled air from the gravity coilfalls and warm air from the products rises. However, such gravity typecooling coils also tend to accumulate frost over time as moisture in theair space within the case (and from the ambient air when doors to thecase are opened) and from the food products condenses and freezes on thesurfaces of the cooling coils.

Accordingly, it would be desirable to provide a refrigerated displaycase of the open-front type that combines the advantages of contactcooling of food products provided by chilled shelves and the advantagesof the humidity control provided by an air curtain, in a way thatminimizes or eliminates the accumulation of frost on the chilledsurfaces (e.g. shelves, air curtain dehumidifying coil, etc.) of therefrigerated case. It would be desirable to provide a refrigerateddisplay case of the open-front type that combines the advantages ofcooling of food products provided by gravity-type cooling coils and theadvantages of the humidity control provided by an air curtain, in a waythat minimizes or eliminates the accumulation of frost on the chilledsurfaces (e.g. gravity cooling coil, air curtain dehumidifying coil,etc.) of the refrigerated case. It would also be desirable to provide arefrigerated display case having a gravity coil and refrigerated shelvesoperating below 32° F. for cooling the products in the storage area andan air curtain dehumidified by an air curtain dehumidifying coiloperating at above 32° F., so that the air curtain cooling coil does notaccumulate frost and the air curtain is sufficiently cool and dry totemper or maintain a low humidity environment within the storage spaceto minimize or eliminate frost accumulation on the chilled shelves orthe gravity coil.

Accordingly, it would be desirable to provide a refrigerated displaycase having any one or more of these or other advantageous features.

SUMMARY

The present invention relates to an open-front refrigerated case withreduced frost operation. The case includes a product storage space andat least one chilled shelf within the storage space. A coolingsystem-provides a coolant for circulation through the chilled shelf. Anair curtain dehumidifying coil operating at a temperature above 32° F.is provided to dehumidify a flow of air that is discharged downwardly inthe form of an air curtain across a front opening of the case tominimize a humidity level within the storage space.

The present invention also relates to an open-front refrigerated displaycase with reduced frost operation. The case includes a product storagespace and a gravity cooling coil disposed in a top portion of thestorage space. A cooling system provides a coolant for circulationthrough the gravity cooling coil. An air curtain dehumidifying coiloperating at a temperature above 32° F. is provided dehumidify a flow ofair that is discharged downwardly in the form of an air curtain across afront opening of the case to minimize a humidity level within thestorage space.

The present invention further relates to an open-front refrigerated casewith reduced frost operation. The case includes a product storage spaceand at least one chilled shelf within the storage space and a gravitycooling coil disposed within a top portion of the storage space. Acooling system provides a coolant for circulation through the chilledshelf and the gravity cooling coil. An air curtain dehumidifying coiloperating at a temperature above 32° F. is provided to dehumidify a flowof air that is discharged downwardly in the form of an air curtainacross a front opening of the case to minimize a humidity level withinthe storage space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a side elevation view of arefrigerated case having chilled shelves within a storage space and anair curtain dehumidified by an air curtain dehumidifying coil operatingabove 32° F. according to one exemplary embodiment.

FIG. 2 is a schematic representation of a side elevation view of arefrigerated case having a gravity cooling coil disposed within a topportion of a storage space and an air curtain dehumidified by an aircurtain dehumidifying coil operating above 32° F. according to anotherexemplary embodiment.

FIG. 3 is a schematic representation of a side elevation view of arefrigerated case having chilled shelves within a storage space, and agravity cooling coil disposed within a top portion of the storage space,and an air curtain dehumidified by an air curtain dehumidifying coiloperating above 32° F. according to another exemplary embodiment.

FIG. 4 is a schematic representation of a side elevation view of arefrigerated case having chilled shelves within a storage space, and agravity cooling coil disposed within a top portion of the storage space,and an air curtain dehumidified by an air curtain dehumidifying coiloperating above 32° F. according to a further exemplary embodiment.

DETAILED DESCRIPTION

Referring to the FIGURES, a front-loading refrigerated case 10 of theopen-front type having a storage space 16 for display of chilled (e.g.refrigerated, frozen, etc.) products is shown according to an exemplaryembodiment. The case 10 is shown to include an air curtain 14 (e.g. airstream, etc.) formed from a flow of air that is dehumidified by an aircurtain dehumidifying coil 24. Unlike conventional air curtains thatfunction to provide primarily a thermal boundary to separate the lowtemperature interior product storage space of the case from a warmerexternal ambient environment surrounding the case (e.g. supermarketatmosphere, etc.), the air curtain of the illustrated embodiments isoperated at an increased temperature and functions primarily as ahumidity tempering device to maintain a low humidity level within thestorage space. The dehumidified air curtain may also provide a secondarybenefit of serving, at least to some degree, as a thermal boundary too.The low temperature of the food products within the storage space ismaintained primarily by contact cooling from chilled shelves and/or thecooling effects from the circulation of air from a gravity cooling coildisposed above the shelves. The operation of the air curtain at anincreased temperature (in relation to conventional open-frontrefrigerated case air curtains) is intended to prevent frostaccumulation on the air curtain dehumidifying coil, while also providingsufficient dehumidification to the air curtain to maintain the productstorage space at low humidity to minimize or eliminate frostaccumulation on the chilled shelves and/or gravity cooling coil(s). Thecombination of the dehumidification provided by the relatively “warmer”air curtain and air curtain dehumidifying coil, with the chilled shelvesand/or gravity cooling coil to maintain the temperature of the productsin the storage space, is believed to provide a relatively “frost-free”or reduced-frost refrigerated case of the open-front type.

Referring to FIGS. 1-4, the operation of the humidity-tempering aircurtain 14 is shown according to an exemplary embodiment. The case 10 isshown to include an air curtain flow path 20 having an airflow device(shown as a fan 22) and a dehumidification device 24 (shown as the aircurtain dehumidifying coil, but may also be a desiccant wheel or otherdehumidification device) for dehumidifying a flow of air that is drawnin through a front portion of the case, and discharged from an exitopening 26 shown along a top front portion of the case. The air curtaindehumidifying coil 24 is shown located in a bottom portion of the caseadjacent to fan 22 and receives a source of coolant from either aprimary cooling system 40 (as shown for example in FIG. 4) or asecondary cooling system 50 (shown for example in FIG. 1). According toan alternative embodiment, the dehumidifying device may be located atanother suitable location, such as within a rear portion of the casehousing, including for example, within air flow passage 20).

Unlike conventional open-front refrigerated cases that use a commoncooling coil to chill an air curtain (to provide a thermal boundaryacross the open front) and to provide chilled air for cooling thestorage space and the products stored therein, the dehumidified aircurtain 14 operates primarily as a humidity boundary and not as theprimary source of cooling for the storage space 16 and the productscontained therein. Thus, the temperature of the air curtain may beoperated at a temperature that is higher than the air curtains ofconventional open-front cases. For the embodiments where thedehumidification device is provided as a coil, the dehumidifying coil 24may receive a supply of coolant from any suitable source.

As shown for example in the embodiment of FIG. 1, the coil 24 receives asupply of a liquid coolant from a secondary liquid coolant system 50,where the temperature of the coolant may be controlled by a chiller 42that interfaces with the primary refrigeration system 40. The chillermay be controlled for operation of one case, or for a plurality of caseshaving similar operating temperature requirements. According to theembodiment shown in FIG. 1, the flow of liquid coolant through the coil24 may be controlled (e.g. “pulsed” on an open-closed manner ormodulated in a variable position manner) by a flow regulating device 28(e.g. valve, etc.) to adjust the rate of liquid coolant flow through thecoil 24. The operation and position of valve 28 may be controlled by anysuitable control system in response to suitable parameters, such as asignal representative of the temperature of the coil 24, a signalrepresentative of the humidity of the air curtain 14, a signalrepresentative of the humidity within the storage space 16, etc.Suitable instrumentation of a conventional type for providing suchsignals (e.g. thermocouples, RTDs, humidity sensors, etc.) may beprovided at appropriate location and arranged to provide a signal to aprogrammable control device such as a microprocessor to provide theappropriate output signal to the valve 28. All such operating andcontrol schemes are intended to be within the scope of the embodimentsdescribed herein.

As shown by way of example in FIG. 4, the coil may alternatively receivea supply of refrigerant coolant from the primary refrigeration system40, which may also include an electronic pressure regulator 45 or asuperheat control valve 43 of a conventional type to control thetemperature of the refrigerant coolant within the coil 24. The primaryrefrigeration system 40 and the secondary liquid coolant system 50 maybe configured in any suitable arrangement to provide the desireddehumidification performance for the air curtain and the desiredtemperature control for the shelves and gravity cooling coils. As shownby way of example in FIG. 4, the primary refrigeration system may beconfigured to supply a refrigerant coolant to the gravity cooling coils32 and to the dehumidification coil 24, while the secondary liquidcoolant system may be configured to provide cooling to shelves 30. Allsuitable combinations of the coils, shelves and coolant supply systemsare intended to be within the scope of the embodiments.

According to the present embodiments, the temperature and flow rate ofthe coolant through the air curtain dehumidifying coil 24 is regulatedso that the dehumidifying coil 24 operates at a temperature abovefreezing (i.e. 32° F.) so that moisture from the flow of air thatcondenses on the coil 24 remains in a liquid state and is routed to asuitable receptacle (e.g. drip pan, etc.) or drain (not shown), and doesnot freeze on the surface of the dehumidifying coil 24. Operation of thedehumidifying coil 24 at a temperature above freezing is intended toprevent frost accumulation on the surface of the air curtaindehumidifying coil 24. The dehumidification of the air curtain 14 isintended to maintain a low humidity level within the storage space 16 bytempering the surrounding ambient air and humidity with a dehumidifiedlayer of air. The air curtain dehumidifying coil 24 dehumidifies theflow of air used in the air curtain 14 to maintain a low humidity levelwithin the storage space 16. The low humidity level within the space 16permits the use of low temperature cooling devices such as (for example)chilled shelves and/or gravity coil(s) to cool the food products, in amanner intended to minimize or eliminate the accumulation of frost onthe surfaces of the shelves or gravity coil(s).

According to another embodiment, the dehumidification device may benon-coolant based and provided as a liquid desiccant, desiccant wheel,or the like, where the dehumidification coil and the supply of a coolantthereto are omitted. The dehumidification device (such as a desiccantwheel) may be arranged within a bottom or rear portion or top portion ofthe case housing for simple and convenient replacement.

Referring to FIG. 1, case 10 is also shown to include chilled(refrigerated, cooled, etc.) shelves 30 mounted within the space 16 andarranged to receive chilled products for storage and display. Thechilled shelves 30 receive a supply of coolant for chilling the shelves.The coolant may be circulated through channels or passages formed withinthe shelves, or may be circulated through tubing or coils contacting (orintegrated with) an underside of the shelf. As shown in the illustratedembodiment of FIG. 1, the coolant may be a chilled liquid coolant, suchas a glycol-based fluid, provided by a secondary liquid cooling system50 that circulates the coolant in a secondary cooling loop 52 to theshelves 30 and to a heat exchange device shown as a chiller 42. Chiller42 is shown to interface with a “primary” cooling system 40, such as arefrigeration system (e.g. a direct expansion or vapor-compression typerefrigeration system, etc.) that operates to chill the coolantcirculating in the secondary cooling loop 52. The primary cooling systemand the secondary cooling system may be provided in any one of multiplecombinations for use with the case (or multiple cases) in a facility.For example, the secondary cooling system may be a local system providedat the particular case location and interfaces with a centrally locatedprimary refrigeration system configured to interface with multiplecases. Also, the secondary cooling system may be provided as acentralized system that supplies coolant to multiple cases within afacility (such as a supermarket, etc.) and is chilled by a single,remotely located primary refrigeration system. According to analternative embodiment, the coolant may be provided directly by a singlerefrigeration system and a “secondary” cooling system may be omitted.

The coolant is provided at a temperature sufficient to permit thechilled shelves 30 to provide a desired amount of contact cooling tofood products (or the like) disposed on the shelves. According to oneembodiment, the temperature range of the coolant provided to the shelves30 is below freezing, for example, within a range of approximately 20°F.-32° F. Alternatively, the temperature range of the coolant providedto the shelves may be above freezing, for example, within a range ofapproximately 32° F.-38° F. However, the coolant may be provided at anysuitable temperature that is appropriate to maintain the desiredtemperature of the products disposed on the shelves within the storagespace. The relatively low humidity level in the case is intended toallow the shelves to operate below freezing without accumulatingexcessive amounts of frost on the surfaces of the shelves.

Referring to FIG. 2, case 10 is also shown to include a gravity coolingcoil 32 disposed within a top portion of the storage space 16 andarranged to receive a supply of coolant to provide cooling to theproducts on conventional shelves 31 located beneath the gravity coil 32.A single gravity coil 32 may be provided at a top portion of the storagespace (as shown) or multiple gravity coils may be provided (e.g. onemounted beneath each shelf, etc.). As shown in the illustratedembodiment of FIG. 2, the coolant may be a chilled liquid coolant, suchas a glycol-based fluid, provided by the secondary cooling system 50that circulates the coolant in secondary cooling loop 52 to the gravitycoil(s) 32 and to the chiller 42. According to an alternativeembodiment, the coolant for the gravity coil(s) may be provided directlyby a refrigeration system and a secondary cooling system may be omitted.

The coolant is provided at a temperature sufficient to permit thegravity coil(s) 32 to provide a desired amount of cooling to the foodproducts (or the like) disposed on the shelves 31. According to oneembodiment, the temperature range of the coolant provided to the gravitycoil(s) 32 is below freezing, for example, within a range ofapproximately 20° F.-32° F. Alternatively, the temperature range of thecoolant provided to the gravity coil(s) may be above freezing, forexample, within a range of approximately 32° F.-38° F. However, thecoolant may be provided at any suitable temperature that is appropriateto maintain the desired temperature of the products within the storagespace. The relatively low humidity level in the case is intended toallow the gravity coils 32 to operate below freezing withoutaccumulating excessive amounts of frost.

Referring to FIG. 3, case 10 is shown to include both chilled shelves 30and a gravity cooling coil 32 disposed within a top portion of thestorage space 16, where the shelves 30 and the gravity coil(s) 32 arearranged to receive a supply of coolant to provide cooling to theproducts on the shelves 30 located beneath the gravity coil(s) 32. Asshown in the illustrated embodiment of FIG. 3, the coolant may be achilled liquid coolant, such as a glycol-based fluid, provided by thesecondary cooling system 50 that circulates the coolant in a secondarycooling loop 52 to the chilled shelves 30 and the gravity coil(s) 32 andto the chiller 42. According to an alternative embodiment, the coolantfor the chilled shelves and the gravity coil(s) may be provided directlyby a refrigeration system and a secondary cooling system may be omitted.

Referring further to FIG. 1 by way of example, the coolant is providedat a temperature sufficient to permit the combination of the chilledshelves 30 and the gravity coil(s) 32 to provide a desired amount ofcooling to the food products (or the like) disposed on the shelves. Theshelves and the gravity coils may have separate flow regulation ortemperature control devices (shown schematically as valves 54) intendedto permit the shelves and the gravity coil(s) to operate at differenttemperatures or coolant flow rates, so that a product cooling profilewithin the storage space of the case can be customized to suit productshaving different temperature storage requirements. The coolant may beprovided at any suitable temperature and flow rate that is appropriateto maintain the desired temperature of the products within the storagespace. The relatively low humidity level in the case is intended toallow the chilled shelves and the gravity coil(s) to operate belowfreezing without accumulating excessive amounts of frost. The valves 54may be operated in any suitable manner, such as “open-closed” or“variable position modulation” to maintain a desired temperature on eachshelf and/or cooling coil. The operation and control of valves 54 andthus temperature of the shelves 30 and coils 32, may be provided by anysuitable control system, such as temperature sensors on the shelvesand/or coils providing signals representative of temperature to aprogrammable control device operable to provide output signals tocontrol position of the valves 54 to maintain a desired temperature ateach shelf and/or gravity cooling coil.

According to any exemplary embodiment, an open-front type refrigerateddisplay case is provided that is intended to operate in a relativelyfrost-free manner in comparison to conventional open-front refrigeratedcases. The case of the illustrated embodiments uses a dehumidificationdevice such as a coil operating at a temperature above freezing (toprevent frosting of the coil) to dehumidify a flow of air for use in anair curtain, where the air curtain functions as a humidity temperingdevice to maintain a relatively low humidity level within the storagespace, while chilled shelves and/or gravity cooling coil(s) are providedwithin the storage space to maintain the desired temperature of foodproducts stored within the space. The dehumidified air curtain isintended to permit operation of the chilled shelves and/or gravitycooling coil(s) in a relatively frost-free manner, by providing ahumidity boundary that minimizes the level of moisture in the air spaceproximate the shelves and/or gravity cooling coil(s). Accordingly, theunique combination of an air curtain dehumidified by a coil operating ata temperature above freezing, and contact or gravity cooling elementswithin the storage space to cool the products has resulted in anopen-front type refrigerated display case that is believed to operate ina manner that substantially reduces the need for defrosting of thecooling surfaces of the case.

According to any alternative embodiment, other types cooling ordehumidifying devices or technology may be used to permit operation ofthe case in a manner that reduces the humidity in the vicinity ofcooling surfaces that operate at a temperature below freezing.Accordingly all such types of cooling and/or dehumidification technologyis intended to be within the scope of the disclosure.

It is also important to note that the construction and arrangement ofthe elements of the refrigerated case with reduced frost operation asshown in the preferred and other exemplary embodiments is illustrativeonly. Although only a few embodiments of the present inventions havebeen described in detail in this disclosure, those skilled in the artwho review this disclosure will readily appreciate that manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multiple partsor elements, the plenum and its inlets, outlets, and airflow devices maybe arranged in any suitable manner or otherwise varied to take advantageof the dehumidified air curtain and the cooling elements within thestorage space. The length or width of the structures and/or members orconnectors or other elements of the case may be varied. It should benoted that the elements and/or assemblies of the refrigerated case maybe constructed from any of a wide variety of materials that providesufficient strength or durability, in any of a wide variety of colors,textures and combinations. Accordingly, all such modifications areintended to be included within the scope of the appended claims. Othersubstitutions, modifications, changes and omissions may be made in thedesign, operating conditions and arrangement of the preferred and otherexemplary embodiments without departing from the spirit of the appendedclaims.

The order or sequence of any process or method steps may be varied orre-sequenced according to alternative embodiments. Anymeans-plus-function clause is intended to cover the structures describedherein as performing the recited function and not only structuralequivalents but also equivalent structures. Other substitutions,modifications, changes and omissions may be made in the design,operating configuration and arrangement of the preferred and otherexemplary embodiments without departing from the spirit of the appendedclaims.

1. An open-front refrigerated case with reduced frost operation,comprising: a housing having an open front and defining a productstorage space therein; an air flow device operatively coupled to an airflow path to direct a flow of air over a dehumidification coil fordischarge as a dehumidified air curtain over the open front, thedehumidification coil operating substantially frost-free at atemperature of greater than 32° F.; at least one of a contact coolingdevice and a gravity cooling device disposed within the space andarranged to receive a coolant from a coolant system; wherein thedehumidified air curtain operates as a humidity tempering boundary tominimize the humidity within the storage space.
 2. The case of claim 1wherein the coolant system comprises a refrigeration system and thecoolant is a refrigerant.
 3. The case of claim 1 wherein the coolantsystem comprises a secondary liquid coolant system.
 4. The case of claim3 wherein the secondary liquid coolant system interfaces with a primaryrefrigeration system through a chiller.
 5. The case of claim 4 whereinthe chiller is contained within the housing.
 6. The case of claim 1wherein the chiller is a centrally located chiller operable for use witha plurality of cases in a facility.
 7. A refrigerated display casecomprising: a housing having an open front and defining a space adaptedto receive products; a dehumidification device operating at atemperature greater than 32° F.; an air flow device operable to direct aflow of air over the dehumidification device and for discharge over theopen front as a dehumidified air curtain; at least one shelf arranged toreceive a flow of a coolant to provide contact cooling to the products;a cooling system providing coolant to the shelf; wherein thedehumidification device operates above freezing in a substantiallyfrost-free manner and the dehumidified air curtain maintains a lowhumidity environment proximate the shelf so that the shelf operates in asubstantially frost-free manner.
 8. The refrigerated display case ofclaim 7 wherein the air flow device comprises a fan, and the fan anddehumidification coil are located in a plenum formed by the housing. 9.The refrigerated display case of claim 7 wherein the coolant comprises arefrigerant.
 10. The refrigerated display case of claim 7 wherein theshelf comprises a plurality of shelves oriented in a vertically stackedarrangement.
 11. The refrigerated display case of claim 10 wherein thecoolant comprises a liquid coolant provided by a secondary coolingsystem that interfaces with a primary cooling system through a heatexchanger.
 12. The refrigerated display case of claim 11 wherein thesecondary coolant system comprises at least one flow regulation deviceoperable to maintain a first shelf at a first temperature and a secondshelf at a second temperature.
 13. The refrigerated display case ofclaim 7 further comprising a gravity cooling coil disposed in a topportion of the space.
 14. The refrigerated display case of claim 7further comprising a gravity cooling coil disposed directly beneath theshelf.
 15. The refrigerated display case of claim 7 wherein thedehumidification device comprises a coil configured to receive a supplyof at least one of the coolant or a refrigerant.
 16. The refrigerateddisplay case of claim 7 wherein the dehumidification device comprises adesiccant wheel.
 17. A refrigerated display case comprising: a housinghaving an open front and defining a space adapted to receive products; afirst coil operating at a temperature greater than 32° F.; an air flowdevice operable to direct a flow of air over the first coil and fordischarge over the open front as a dehumidified air curtain; a secondcoil operating at a temperature below 32° F., the second coil disposedwithin the space to cool the products; a cooling system providingcoolant to the second coil; wherein the first coil operates abovefreezing in a substantially frost-free manner and the dehumidified aircurtain maintains a low humidity environment proximate the second coilso that the second coil operates in a substantially frost-free manner.18. The refrigerated display case of claim 17 wherein the first coilcomprises a dehumidification coil disposed external to the space andadjacent to the air flow device.
 19. The refrigerated display case ofclaim 17 wherein the second coil comprises a gravity cooling coildisposed in a top portion of the space.
 20. The refrigerated displaycase of claim 17 further comprising a shelf disposed within the spaceand the low humidity environment and configured to receive the products.21. The refrigerated display case of claim 20 wherein the shelf isconfigured to receive a supply of the coolant to provide contact coolingto the products and.
 22. The refrigerated display case of claim 21wherein the shelf operates in a substantially frost-free manner in thelow humidity environment.
 23. The refrigerated display case of claim 22further comprising a third coil disposed beneath the shelf andconfigured to receive a supply of the coolant, the third shelf arrangedas a gravity cooling coil and operating in a substantially frost-free inthe low humidity environment.
 24. A method of operating a refrigerateddisplay case for low frost performance, comprising: providing a housingdefining a storage space for products, the storage space having an openfront, and an air flow passage communicating with the open front;providing a dehumidification coil communicating with the air flowpassage; providing an air flow device operable to direct a flow of airover the dehumidification coil for discharge as a dehumidified aircurtain over the open front; providing a cooling device comprising atleast one of a contact-cooling shelf and a gravity cooling coil withinthe space for cooling products; circulating a coolant to the coolingdevice; and operating the dehumidification coil at a temperature above32° F.
 25. The method of claim 24, further comprising the step ofcirculating a refrigerant through the dehumidification coil.
 26. Themethod of claim 24 wherein the cooling device comprises a contactcooling shelf and a gravity cooling coil, and the coolant circulated tothe contact cooling shelf comprises a liquid coolant and the coolantcirculated to the gravity cooling coil comprises a refrigerant.